1. Field of the Invention
The present invention relates to a luminescent device capable of emitting light by converting electric energy into light, in particular, relates to an organic electroluminescent device (“luminescent device” or “EL device”).
2. Description of the Related Art
Organic electroluminescent devices are attracting public attention as promising display devices for capable of emitting light of high luminance with low voltage. An important characteristic of organic electroluminescent devices is consumed electric power. Consumed electric power is represented by: [Consumed electric power=Voltage×electric current], so that the lower the value of voltage that is necessary to obtain desired brightness and the smaller the value of electric current, the lower is the consumed electric power of the device.
As one trial to lower the value of electric current that flows to a device, a luminescent device utilizing luminescence from ortho-metalated iridium complex (Ir(ppy)3: Tris-Ortho-Metalated Complex of Iridium(III) with 2-Phenylpyridine) is reported (e.g., refer to JP-A-2001-247859 (The term “JP-A” as used herein refers to an “unexamined published Japanese patent application”.)). The phosphorescent devices described therein are greatly improved in external quantum efficiency as compared with conventional singlet luminescent devices, and have succeeded in making the value of electric current smaller.
An example to use a phenylpyrazole coordinated iridium complex as a light-emitting material in a blue phosphorescent device is reported (e.g., refer to U.S. 2001/0019782). However, a phenylpyrazole coordinated iridium complex is low in emission quantum efficiency, so that further improvement is desired.
From the viewpoint of the improvement of luminous efficacy of a phenylpyrazole coordinated iridium complex, a biphenylpyrazole coordinated iridium complex is reported (WO 04/085450), but further improvement is required in the points of high luminous efficacy, blue emission of high color purity (maximum luminescent wavelength: 465 nm or less), and long duration of life of devices.